Once, about 1,500 years ago, an essentially urban culture existed in what is now jungle settled by scattered tribes, researchers report in Friday's edition of the journal Science.

They weren't as sophisticated as well-known cultures like the Maya to the north, but their culture was more complex than anthropologists had thought.

The find "requires a rethinking of what early urbanism may have been like, in diverse and variant forms," said Michael J. Heckenberger of the University of Florida, lead author of the study.

Heckenberger and colleagues first reported evidence of the culture  which he calls Xingu after the local river  in 2003 and now have unearthed details of the ancient communities.

The researchers found evidence of 28 prehistoric residential sites. Initial colonization began about 1,500 years ago, and the villages they studied were dated to between 750 and 450 years ago. The local population declined sharply after Europeans arrived.

Villages were distinguished by surrounding ditches, with berms on the inside made from material dug from the ditch and topped with a wooden palisade wall, Heckenberger reported.

Each village had a central plaza, the team reports. Larger communities could cover 150 acres and included gates and secondary plazas.

And each settlement had a formal road connected to the central plaza and oriented northeast to southwest, the direction of the summer solstice.

Populations were estimated at 800 to 1,000 in the towns, with satellite farming villages bringing the total to about 2,500 in each of several village clusters.